Vehicle suspension system

ABSTRACT

A vehicle suspension system which incorporates a novel variable rate rear suspension spring having two effective stages arranged such that the natural frequency will increase or decrease substantially the same amount as the natural frequency of the front suspension system will increase or decrease when load is added or removed. The rear suspension spring includes a first stage which combines both a constant pitch section and an increasing pitch section, and a second stage which comprises only the constant pitch section. The suspension system embodying the rear suspension springs of the foregoing character operates to maintain the front suspension natural frequency substantially equal to the rear suspension natural frequency under all loading conditions.

United States Patent 11 1 Scheublein et a]. Nov. 20, 1973 VEHICLESUSPENSION SYSTEM Primary ExaminerPhilip Goodman [75] Inventors: JamesK. Scheublein; Gary D. Attorney predenck woodmff et Swmney, both of St.Lou1s, lvlo. ABSTRACT I [73l Asslgnee: Moog lndustl'ieslnc-ist-LOUIS'MO' A vehicle suspension system which incorporates a [22] Filed;Jam 3 7 novel variable rate rear suspension spring having two effectivestages arranged such that the natural fre- [211 Appl' quency willincrease or decrease substantially the same amount as the naturalfrequency of the front [52] US. Cl. 280/124 R, 267/60 suspension systemwill increase or decrease when [5 1] Int. Cl. B60g 11/16 load is addedor removed. The rear suspension spring [58] Field of Search 280/124 R;267/60, includes a first stage which combines both a constant 267/180,166 pitch section and an increasing pitch section, and a second stagewhich comprises only the constant pitch References Cited section. Thesuspension system embodying the rear UNITED STATES PATENTS suspensionsprings of the foregoing character op- 3,572,678 3 1971 Jerz 267/60crates to maintain the from Suspension natural 3,486,763 12/1969 Hexel280/124 R quency substantially equal to the rear suspension 3,345,07910/1967 Wickham 267/180 X natural frequency under all loadingconditions.

6 Claims, 4 Drawing Figures PATENTEDRQV 20 mm 37731346 SHEET 1G? 2SECOND 57/265 401/54? mm P/i'C/l F/P'l' $54 5 Y CONSTHNT p/ TCH LPIC-3.2

VEHICLE SUSPENSION SYSTEM BRIEF RESUME OF THE INVENTION This inventionrelates to vehicle suspension systems and is particularly concerned withthe provision of novel suspension springs in order to maintain the totalvehicle suspension in balance, whereby substantially the same ridecharacteristic under all load conditions is maintained. The inventionalso relates to a suspension spring that will allow increase in the loadcarrying capacity of the vehicle without changing the original operatingcharacteristics of such vehicle.

It is generally known that common vehicle designs strive for asuspension system such that the optimum ride characteristics areobtained when the vehicle is carrying two people in the front seat andwith no load in the trunk other than the usual spare tire and jackequipment. It is also known that the ride characteristics rapidlydeteriorate as load is applied to the vehicle, such as temporary objectsplaced in the trunk. Therefore, an objective of this variable rate coilspring is to maintain the optimum ride characteristics under all loadconditions by keeping the front and rear suspensions in balance. Thisobjective is well satisfied through a rear spring having a variable ratewith two effective stages where the rate increases with respect to loadand with respect to deflection such that the front suspension and rearsuspension natural frequency will be equal under all load conditions. Itis also an objective to increase the load carrying capacity of a vehicleand this is found to be automatically satisfiedby the two effectivestages characteristic for maintaining the vehicle suspension in balanceor tune.

The limited concept of varying the rate of a coil spring is known fromprevious usage of variable rate springs, but the idea of a plannedvarying rate spring having two efiective stages compatible to anautomotive suspension system and its unique loading characteristics isnew and different. The design intentions of the older variable ratesprings were either to maintain constant frequency of the individualspring-mass system or to limit deflection under load. The completeautomotive suspension system was never considered. This inventionrelates to maintaining the front suspension natural frequency equal toor balanced with the rear suspension natural frequencyunder all loadingconditions. The front suspension natural frequency is not constant, butit will vary under various loading.

The spring design of this invention requires a percent of the totalcoils to be cancelled just by the normal vehicle weight. This design hasnot been achieved before and first appears to be a waste of steel, butthe gain in lower noise level, caused by coil clash, anda gradual rateincrease under all loads far outweights the steel cost. The addition ofa coating of suitable material, such as a vinyl coating, decreases noiseand for this application it is new.

BRIEF DESCRIPTION OF THE DRAWINGS The present improvements in vehiclerear variable wherein:

FIG. 1 is a schematic side velevational view of a pas: senger typevehicle with the various components and symbols indicated thereon;

FIG. 2 is a greatly enlarged elevationalview of a variable rate coilspring of the character to be referred to hereinafter for application asthe rear suspension springs for the vehicle of FIG. 1;

FIG. 3 is a graph to illustrate the principle of the variable ratespring characteristics for the coil spring seen in FIG. 2; and

FIG. 4 is a graph to relate the natural frequency of both front and rearsuspension systems with weight added to the trunk space of a passengertype vehicle.

DESCRIPTION OF THE EMBODIMENTS In FIG. 1 there is represented apassenger type vehicle having a body or sprung mass 10 with its centerof gravity represented at the center of gravity point CG which is alsothe location of the normal weight P with two passengers seated in thefront seat and no load added in the trunk other than the usual sparetire and jack. Front wheels 1 l are connected to the body by coilsprings 12 having a rate K, and rear wheels 13 are connected to the bodyby coil springs 14 having a rate K The trunk space 15 in the body 10 isshown with an added load W located at a distance b behind the rear wheelaxle. The axle for the front wheels 11 is located a distance L, from thecenter of gravity, and the axle for the rear wheels 13 is located at-adistance L behind the center of gravity.

In this vehicle of FIG. 1 the front coil springs 12 have a rate K, whichis the effective force that is required to raise the wheels one inch. Inlike manner the rate of the rear coil springs 14 is K When the load W isplaced in the trunk it has the effect of shifting the center of gravityor CG rearwardly so that L, increases and L decreases. Thus, it can beseen that there is a definite relation between the front and rear springrates in order to achieve a smooth, comfortable ride. This concept isreferred to as suspension tuning and is expressed by the followingequation:

Where L, L, when W 0 When constant rate springs are employed at thefront and rear, as is the rule today in vehicle systems, the addition ofthe load W causes the suspension springs to go out of balance. However,when the proposed variable rate spring is employed for the rear wheelsuspension,

the overall suspension system remains tuned and in balance. Whilevariable rate springs have been proposed in the past, none has been ableto maintain a tuned suspension for a variety of loads in the trunk. Theautomotive industry normally has designed a vehicle suspension such thatthe optimum ride characteristics are obtained when the vehicle iscarrying two average weight riders in the front seat and only the sparetire and jack in the rear or trunk. It is known, however, that the ridecharacteristics rapidly deterioriate as additional load is placed in therear trunk space. Thus, it is the purpose of this invention to maintainthe optimum ride characteristics as load is added to the rear trunkspace by keeping the front and rear wheel suspensions in tune andbalance. Investigation of the problem has shown that a tuned or balancedsuspension is. achieved through the use of rear variable rate springswhere the rate increases with respect to load increases and with respectto deflection according to equation 2. Therefore, it is found thatincreased load carrying capacity is achieved automatically by theincreasing rear spring rate.

The variable rate objective is applied to a vehicle rear coil spring byproviding a two stage spring, where the first stage comprises the actionof the entire spring and the second stage has a substantially constantpitch. Such a spring 14 is illustrated in FIG. 2 where a portion of thecoils in the spring have an increasing pitch and are spaced such thatthe rate increases according to equation 2.

The various terms in the foregoing equation are illustrated andexplained in connection with the description of FIG. 1. The principlehere is thatthe rear spring 14 must have a variable rate to maintain thesuspension tuned and in balance. For maximum load carrying ability ofthe vehicle 10 the front springs 12 are held to a constant rate whilethe rear springs 14 have a variable rate.

It has been found through complicated mathematical analysis that bothoptimum ride characteristics under load and increased load capability ofthe vehicle are satisfied together. It has also been found that thevariable rate spring which satisfies the foregoing requirements needs tohave a percentage of the total coils cancelled out just by the normalvehicle weight. This apparently has not appeared before and might beconsidered a waste of steel, but it improves the operation of the coilspring by lowering the noise level caused by coil clash, while leadingto a gradual rate increase under all loads imposed on the vehicle. Thecoil clash referred to is understood to be produced by adjacent coilshammering on each other as load is applied and released. This isespecially noticeable where the coil turns are relatively close togetherand have a very low pitch.

In producing a variable rate coil spring for use with passengervehicles, for example, it has been found that it is easiest to produce aspring having linearly increasing pitch. Such a spring yields a naturalfrequency which is not constant for all loads.

The suspension system for the vehicle depicted in FIG. 1 includes frontsuspension coil springs 12 which have a constant pitch and aconstantrate, and rear coil springs 14 which have a linearly increasingpitch at cer tain coils and a constant pitch at other coils so that therate of the front and rear coil springs varies in a manner that willkeep the suspension in balance under all loading conditions. A typicalrear suspension spring has been illustrated in FIG. 2. The example shownis of a spring having a coil diameter of 5.50 inches. It is formed fromstock having a diameter of 0.705 inches.

4 The coil has a constant pitch of three inches, for two turns up fromthe bottom seat, portion. Thereafter the coil turns have a variablepitch as indicated for the next three turns. i i

The balance characteristics referred to here by definition is achievedby maintaining the front suspension natural frequency equal to the rearsuspension natural frequency. This can be mathern'atically'expressed inthe form K L K L The front suspension generally has a constant rate, butnot a constant natural "frequency. Thus, as load is added to the trunkof the vehicle, the loading on the front suspension 'decreases'Therefore, the natural frequency of the rear suspension mustvary as load is applied in the trunk in accordance with the change innatural frequency of the front suspension. This can be mathematicallyshown and has been referred to above in equation 1.

In the graph of FIG. 4 the natural frequency of the front suspension isplotted against the load W placed in the vehicle trunk space. It hasbeen stated that in order to maintain balance of the total vehiclesuspension under all load conditions the natural frequency of the rearsuspension must be equal to the natural frequency of the frontsuspension. Therefore, the graph in FIG. 4 is also a plot of the naturalfrequency of the rear suspension against the load W added in the trunkspace for the proposed variable rate spring. In order to meet thiscondition a relationship must exist between the load W added in thetrunk space and the rate of the rear suspension spring. In the graph ofFIG. 3 the rear suspension spring rate in pounds per inch of deflectionis plotted against the load W placed in the vehicle trunk space 15.

While the foregoing description has related to a suspension systememploying coil springs, it is evident that a leaf spring system can beemployed with similar results where the front and rear springs havesubstantially equal natural frequencies, the front spring naturalfrequency varies with loading and the rear spring has variable ratecharacteristics as described. 7

What is claimed is:

1. In a vehicle, a frame having a principal suspension system consistingof a front wheel set, first resilient spring means operably connectingsaid front wheel set to the vehicle frame, av rear wheel set, secondresilient spring means operably connecting said rear wheel set to thevehicle frame, said frame supporting an applied load of a variableamountand disposition relative to said front and rear wheel sets, said firstresilient spring means having a natural frequency which varies with thevehicle loading amount and disposition conditions, and saidsecondresilient spring means having a natural frequency varying with thevariations of said first resilient spring means such that the naturalfrequencies of said first and second resilient spring means remainsubstantially balanced with the loading conditions.

2. The suspension system of claim 1 wherein said second resilient springmeans include sections having a constant pitch and other sections havinga variable pitch.

3. The suspension system of claim 1 wherein the vehicle has its centerof gravity between said front and rear wheel sets, and said secondresilient spring means has a variable rate operative in relation to saidfirst resilient spring means to maintain a substantially balanced systemfor a variety of loads'applied-to the vehicle adjacent said rear wheelset.

4. A suspension assembly for a vehicle consisting of a front wheel setconnected to the vehicle ahead of the center of gravity and a rear wheelset connected to the vehicle behind the center of gravity, front coilsuspension spring means connecting said front wheel set to the vehicle,said front coil springs having a constant rate K rear coil suspensionspring means connecting said rear wheel set to the vehicle, said rearcoil springs having a variable rate K and said front and rear coilsuspension springs having substantially equal natural frequencies forchanges in the loading of the vehicle and said real coil suspensionsprings having a spring rate that varies with load applied to thevehicle.

5. In a vehicle suspension system, a longitudinal frame having a normalload center of gravity, front and rear wheels for said frame, principalsuspension means connecting said front wheels to the foreport of saidframe a predetermined distance L from the center of gravity and having asubstantially constant rate K and principal coil suspension springsconnecting said rear wheel to the rear part of said frame apredetermined distance L from the center of gravity, said principal coilsuspension springs having a portion of the coils formed with a constantpitch and another portion with an increasing pitch such that the rate Kof said suspension springs increases with applied load according to theformula K K [(L L b) W L p ]/[L p bW] 6. In a vehicle, a longitudinalbody frame, from supporting wheels resiliently connected to the forepartof said body frame, said resilient connection of said front wheelscomprising principal coil springs having a substantially constant rate,rear wheels for said body frame, principal coil suspension springsoperatively connected between said rear wheels and the rear part of saidbody frame, said rear wheel coil springs having a linear increasingpitch for certain of its coils and constant pitch for certain others ofits coils such that the rate of said coil springs varies in a manner tomaintain the front and rear portion of said body frame in balance underall loading conditions, and said vehicle having the center of gravity,due to normal load only, located a distance L from the front wheels, therear wheels located a distance L, from the center of gravity, the frontwheel coil springs having a constant rate K the rear wheel coil springshaving a variable rate K and the rate K increasing with load inaccordance with the relation

1. In a vehicle, a frame having a principal suspension system consistingof a front wheel set, first resilient spring means operably connectingsaid front wheel set to the vehicle frame, a rear wheel set, secondresilient spring means operably connecting said rear wheel set to thevehicle frame, said frame supporting an applied load of a variableamount and disposition relative to said front and rear wheel sets, saidfirst resilient spring means having a natural frequency which varieswith the vehicle loading amount and disposition conditions, and saidsecond resilient spring means having a natural frequency varying withthe variations of said first resilient spring means such that thenatural frequencies of said first and second resilient spring meansremain substantially balanced with the loading conditions.
 2. Thesuspension system of claim 1 wherein said second resilient spring meansinclude sections having a constant pitch and other sections having avariable pitch.
 3. The suspension system of claim 1 wherein the vehiclehas its center of gravity between said front and rear wheel sets, andsaid second resilient spring means has a variable rate operative inrelation to said first resilient spring means to maintain asubstantially balanced system for a variety of loads applied to thevehicle adjacent said rear wheel set.
 4. A suspension assembly for avehicle consisting of a front wheel set connected to the vehicle aheadof the center of gravity and a rear wheel set connected to the vehiclebehind the center of gravity, front coil suspension spring meansconnecting said front wheel set to the vehicle, said front coil springshaving a constant rate K1, rear coil suspension spring means connectingsaid rear wheel set to the vehicle, said rear coil springs having avariable rate K2, and said front and rear coil suspension springs havingsubstantially equal natural frequencies for changes in the loading ofthe vehicle and said real coil suspension springs having a spring ratethat varies with load applied to the vehicle.
 5. In a vehicle suspensionsystem, a longitudinal frame having a normal load center of gravity,front and rear wheels for said frame, principal suspension meansconnecting said front wheels to the foreport of said frame apredetermined distance L1 from the center of gravity and having asubstantially Constant rate K1, and principal coil suspension springsconnecting said rear wheel to the rear part of said frame apredetermined distance L2 from the center of gravity, said principalcoil suspension springs having a portion of the coils formed with aconstant pitch and another portion with an increasing pitch such thatthe rate K2 of said suspension springs increases with applied loadaccording to the formula K2 K1 ((L1 + L2 + b) W + L1 p )/(L2 p - bW) 6.In a vehicle, a longitudinal body frame, front supporting wheelsresiliently connected to the forepart of said body frame, said resilientconnection of said front wheels comprising principal coil springs havinga substantially constant rate, rear wheels for said body frame,principal coil suspension springs operatively connected between saidrear wheels and the rear part of said body frame, said rear wheel coilsprings having a linear increasing pitch for certain of its coils andconstant pitch for certain others of its coils such that the rate ofsaid coil springs varies in a manner to maintain the front and rearportion of said body frame in balance under all loading conditions, andsaid vehicle having the center of gravity, due to normal load only,located a distance L1 from the front wheels, the rear wheels located adistance L2 from the center of gravity, the front wheel coil springshaving a constant rate K1, the rear wheel coil springs having a variablerate K2, and the rate K2 increasing with load in accordance with therelation K2 K1 ((L1 + L2 + b) W + L1 p )/(L2 p - bW)